This is a line scanning motor and mirror
from a 1938 Scophony mechanicaly scanned projection
television set. In the early days of TV, cathode ray
tubes (CRTs) were mainly small and dim, only suitable for
viewing in low light levels. To get a large bright
picture, Scophony developed a projection system using a
high intensity mercury vapour lamp. The light was
modulated by a Jefferies cell, and then scanned across
the screen by two mirror drums, a small high speed one
such as this to produce the line scan, and a large slow
speed unit to produce the frame scan (12 mirrors rotating
at 250rpm). The type 123 consists of two motors running
on the same shaft, a standard induction motor to bring
the unit up to speed, and a Phonic motor (in reality
another synchronous motor, but designed to work with High
frequencies) which was synchronised to the Line pulses of
the incoming signal the motors turned a mirror drum with
20 segments (visible at the top of the unit) at 30375rpm
to produce the 405 line picture. For more details of the
system see Scophony
Systems and TVHistory.tv